The casting that turned boating upside down

By Kim Phelan, a Contributing Editor to Casting Source, a publication of the American Foundry Society.

A revolutionary concept in marine engine design called for a special kind of front housing casting that took equal parts of designer and foundry ingenuity and collaboration to pull off.

The announcement was out: Recreational products manufacturer BRP was discontinuing its iconic Evinrude line of outboard engines. For employees at the Sturtevant, Wisconsin, plant that built them, the landscape was changing. A hint in the company’s official press release on May 27, 2020, lifted the curtain hem on something brewing that might just take the boating industry by storm. Way at the bottom of the statement was a curious reference to a next generation marine engine technology called “Project Ghost,” an internal code name for a new product they believed would transform recreational boating.

Until then, boat manufacturers and their customers had two options: An outboard engine that sits prominently (and even obtrusively) at the rear of the boat close to where passengers sit, or a stern drive/inboard engine that’s housed somewhere inside the boat, taking up precious, though unseen, cargo space. BRP conceptualised a third, unheard of alternative they called stealth technology – an outboard engine that is fully and unobtrusively integrated with the boat, virtually out of sight and out of mind.

To achieve such a feat would, in part, require a complex front housing casting to hold the lower unit and gearbox assembly that enables a 150hp engine to reside sleekly below the boat. The BRP team – comprising Supplier Quality Development Engineer Dave Palmer, also an instructor of AFS technical programmes; Product Designer Roger Raetzman; and Senior Buyer Jim Milam – eventually selected AFS Corporate Member LeSueur Inc. (LSI), LeSueur, Minnesota, to produce the 76lb. aluminium (A356) casting that measures 28.33” long x 21.98” wide x 23.80” high.

“I’m pleased that we were able to easily integrate this casting into production,” Palmer reflected. “This is a challenging casting. And it’s a big casting. It needs to be dimensionally accurate, have effective structural properties and be cosmetically appealing. This housing is a testament to the great collaboration that we’ve had with LSI.”

Known commercially as Rotax S, the outboard engine is currently available on BRP’s Manitou pontoon boats, its Alumacraft fishing boats, as well as its Australian brand of Quintrex boats.

Brains Plus Beauty
Fitting the Rotax S outboard engine underneath a boat’s swim platform would mean BRP engineers would have to take a traditional outboard engine and essentially turn it on its side. To do so, they replaced a typical vertical crankshaft with a horizontal crankshaft, which reduced the engine’s overall height. The output of the horizontal crankshaft would then be channelled through a gearbox down to the outboard’s lower unit.

“When you stand next to some of the big new outboards today, you feel like you’re about three feet tall because the engine is just so tall,” said Palmer. “Putting the crankshaft in a horizontal orientation allows us to keep within that profile to be able to fit the engine under the deck. This means, we have to have an additional gearbox, made at BRP’s lost foam foundry in Spruce Pine, North Carolina, to take the output of that crankshaft down to the propeller shaft.”

“The front housing that LeSueur makes is what holds all of this together, so it’s really an important casting,” Palmer continued. “That’s really what’s allowing us to make an outboard engine like this with a horizontal crankshaft, and it’s a brand-new part for us – I mean, this is something completely revolutionary.”

Besides the innovative engineering to reconfigure engine parts for a slimmer, “stealth” fit below deck, the casting required excellent cosmetic features, which low pressure permanent mould was better equipped to handle than lost foam, which had been considered. But why does an under-the-boat engine need to look good?

“It’s not necessarily visible when you’re on the boat, but it is when you’re in the showroom,” said Palmer. “And that’s equally if not more important, because if the customer doesn’t like the way it looks in the showroom, they’re not likely to buy the boat or see it in the water.”

Knowing the casting must retain its corrosion resistance and beauty for many years, the casting’s coating supply chain is elaborate. Once delivered, BRP machines the parts and applies chromate conversion coating. From there, an e-coat is applied and it is painted before it is ready for final assembly.

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